BIFET operational amplifiers combine JFET input transistors with bipolar transistors in a monolithic integrated circuit. The ion-implantation process used in making BIFET devices results in closely matched transistors. This permits true class-AB operation in the output stage which results in near zero crossover distortion and low total harmonic distortion.
In addition to high input impedance (1012 0) and input bias currents in the picoampere range, most BIFET operational amplfiers have slew rates of approximately 13 V/p.s and a typical unity-gain bandwidth of 3 MHz. However, BIFET operational amplifiers have higher offset voltages and input noise than bipolar operational amplifiers.
Some BIFET operational amplifiers are power adjustable. This allows the user to select (with an external resistor) the operating current levels. While this causes a tradeoff with power dissipation, it gives greater control over slew rate or signal bandwidth. An example of such a device is the TL066 BIFET operational amplifier. The TL066 can be adjusted for a no-signal supply current of 5 to 200 uA. Slew rate and bandwidth will also change depending upon the level of operating current. Except for the adjustable feature, the TL066 is similar to the TL06I. The key application for power adjustable operational amplifiers is in battery-operated and telecommunication equipment where power consumption is an important factor. Table 2-2 is a selection guide listing the major parameters to be considered when choosing a BIFET operational amplifier for a particular application.
Table 2-2. BIFET Operational Amplifier Comparison Chart
Test conditions are Vee = ± 15 V. All values are typical.